According to a prior art process, oil containing seeds are heated in so-called cookers or flour boilers in the presence of moisture. Such a flour boiler consists of a vessel with a plurality of hollow plates disposed over each other, each provided with a passage opening for discharge material onto a plate situated thereunder. The oil containing seeds are essentially indirectly heated by the plates.
In order to extract oil from oil containing vegetable raw materials, like fruits or seeds, by squeezing or extracting by means of solvents it is necessary to expose these raw materials previously to a number of pre-treatments. Irrespective of the specific pre-treatments for each kind of seed and the differences owing to a choice between extracting or crushing, the following examples of pretreatments can be mentioned in arbitrary order of succession, i.e.: removal of shells, skins or husks, pulverizing, rolling, heating, drying and cooling.
In dependance of the raw material and the oil extraction process proper, one or more of these pre-treatments are required and some of them even simultaneously. Although the mechanisms between pre-treatment and oil-extraction are not yet entirely known one may explain that the pre-treatments effectuate that:
Cell material is opened, whereby the oil is more easily released; PA1 Undesired components such as albumins, mucous materials and the like are fixed and become insoluble; PA1 The rests of the cell walls are strengthened.
The known process suffers, however, from the disadvantage that the residence time of the product in the cookers or flour boilers often exceeds the optimally necessary time, while moreover a uniform well controlled treatment of the particles is impossible. This is caused by the very bad heat conduction and heat transfer, owing to the fact that in the known process the heat supply is substantially indirect, as it is effected through a heat exchanging surface, while besides, the heat conductivity of the product to be treated is very insufficient, because it is material in bulk that is exposed to the treatments.